The present invention relates to improvements in a method and apparatus for correcting a battery characteristic and for estimating a residual energy of a battery for an electric vehicle.
Generally, an electric vehicle is provided with a residual energy meter for informing a residual energy amount of a battery to a driver. Such a residual energy meter is normally required to have an appearance which is similar to that of a conventional fuel meter of an automotive vehicle equipped with an internal combustion engine. In case that such a conventional residual energy meter is arranged so as to obtain a residual energy (residual energy amount) of a battery by subtracting a discharged total power amount from a battery full capacity, a dischargeable amount from a full capacity (full charged) condition to a zero-power condition or a predetermined amount is used as a battery full capacity. For example, a relationship Wh(P) between a power P and a discharged power amount Wh, which is represented by a graph shown in FIG. 11, is employed to represent a residual energy of the battery. In this graph, the residual energy is a difference between a dischargeable power amount Wh(0) and a discharged amount IWh such that (residual capacity)=Wh(0)--IWh, wherein Iwh is an integrating amount of discharged power which is obtained by a predetermined calculating method using a current I and a voltage V of the battery. The dischargeable power amount Wh(0) employed in the above-mentioned equation is calculated on the basis of an initial characteristic of the battery put in the ordinary temperature.
However, since the dischargeable power amount Wh(0) is varied according to the change of the temperature and the deterioration of the battery, the residual energy which is calculated from the dischargeable power amount Wh(0) obtained on the basis of the initial battery characteristic, will generate a great different from an actual residual energy. This will cause a problem such that the residual energy meter cannot indicate an accurate residual energy. Further, since the discharged power amount at present time is obtained from the integrating amount of discharged power, the estimation accuracy of the residual energy is degraded according to the increase of the capacity of the battery due to the integration of various errors. Further, although the electric vehicle requires a minimum power Pmin for normally continuing the traveling thereof, the discharged power amount or discharged electric amount to zero is employed as a battery capacity. Therefore, the electric vehicle may suddenly stop traveling by a momentary voltage drop of the battery even if the residual energy meter indicates a value greater than zero.